1. Field of the Invention
The present invention generally relates to a radio signal detecting system capable of detecting a radio signal reflected from a target. More specifically, the present invention is directed to a compact radio signal detecting system capable of measuring a distance from the target and a direction of the target, and also capable of detecting azimuth of an incoming radio signal transmitted from other radio signal transmitter.
2. Description of the Prior Art
Radar systems have been widely utilized in air crafts and ships in order to navigate these vehicles and to confirm present positions of the vehicles with respect to a target, and also utilized in meteorological observations. Typically, in a radar system employed in one ship, an electromagnetic wave in a pulse form such as a microwave pulse signal, is transmitted from an antenna at a speed of 300,000 km/sec., and this pulse signal impinges other ships and a land. Then, pulse signals are reflected from these objects and processed to measure distances between this ship and other ships. These measured distances are displayed on a CRT display screen.
This type of conventional marine radar system comprises a large-scale transmitter apparatus with employment of a magnetron and the like, a bulky rotary slot antenna having a length of 1 to 3 m and an antenna unit, a display apparatus equipped with an after-image type large CRT screen, and a motor unit for rotating the slot antenna. Accordingly, this marine radar system has various merits, e.g., high power, high precision, and hard operation conditions. However, there are drawbacks such as a bulky system and high power consumption.
On the other hand, in commercial ships such as fishing boats and container carrier ships, and salvage stations, azimuth detecting systems are utilized to correctly detect azimuth of a signal radiation source by measuring azimuth of an incoming radio signal having a specific frequency. In the azimuth detecting system, the incoming radio signals are received by the first loop-shaped antenna and the second vertically-arranged antenna. The first loop antenna is rotated to receive the radio signals at every preselected rotation angle, and field strengths of these received radio signals are measured. Then, the direction of one radio signal having the highest field strength is detected as the direction of the incoming radio signal reflected from the target. Since this first loop, antenna inherently owns such an antenna characteristic that the field strengths become high when the first loop antenna is located at 90.degree. and 270.degree. with respect to the direction of the incoming radio signal, a decision is made which incoming signal angle corresponds to the incoming direction of the radio signal based upon directivity of the second antenna. In other words, the radio signal received by the first loop antenna is synthesized with the radio signal received by the second antenna, thereby determing the incoming direction of the radio signal. Thereafter, the synthesized signal is amplified, and the field strengths of the synthesized signal with regard to the rotation angles of the first loop antenna are displayed on a CRT display screen as a circular graphic representation.
However, the above-described conventional azimuth detecting systems have similar problems to those of the conventional radar systems. That is, very high technology is required to operate such conventional azimuth detecting systems, so that only well skilled operators can handle these azimuth detecting systems.